Recurring costs, as mentioned, include fuel, oil, annual inspections, and hanger/tie-down. Annual inspections are the most expensive predictable cost (there will be surprises) and will vary depending on what kind of aircraft you buy from about $700 a year on up.

Here's the real surprise, if you purchase a plane and keep it maintained you will likely be able to sell it for more than you paid for it. Especially now as prices are depressed along with most "luxury" items in the economy. I bought a single engine plane for my family to fly in and kept it for ten years before we decided it was time for a change. At one time it was valued at well over twice what I paid for it and I ended up selling it last summer at about 1.8 times my initial purchase price. I only did routine maintenance and some minor upgrades. I also saved money by having friends who could help me out with annual inspections and such, which kept overall costs down.

Notice that if you get one that is going to be a maintenance hog then you may not break even. A wise airplane purchase, however, can almost always be sold after several years for more than it was bought for.

YMMV